(1) Field of the Invention
The present invention relates to a received-light amplifier, and particularly to a photoelectric converting apparatus with a built-in light-receiving device.
(2) Description of the Related Art
In response to the increase in disk revolution speed during the reading of data, as well as the writing of data into various types of optical discs in optical disc apparatuses represented by the DVD-R drive apparatus and Blu-ray disc apparatus, in recent years there has been a demand for a received-light amplifier that can precisely amplify both the high frequency signal during data reading and the pulse signal during data writing. Such a received-light amplifier can be implemented through the shifting of the frequency band and the output voltage in accordance with the input signal.
FIG. 1 is a circuit diagram of the received-light amplifier described in Japanese Unexamined Patent Application Publication No. 08-154023.
This received-light amplifier includes the light-receiving device PD, the current-voltage conversion circuit 10, and the voltage amplification circuit 20.
In the current-voltage conversion circuit 10, the inverting input terminal of an operational amplifier 11 is connected to the cathode of the light-receiving device PD. The anode of the light-receiving device PD is grounded. Plural feedback resistors Rg-a, Rg-b are connected between the inverting input terminal and the output terminal of the operational amplifier 11, and respective feedback capacitors Ca and Cb are connected in parallel to each conversion resistor. In addition, the switch SW1, which selects a feedback resistor, is inserted between the feedback resistor Rg-b and the output terminal of the operational amplifier 11. A reference voltage source Vref is connected to the non-inverting input terminal of the operational amplifier 11. Resistors Rref-a and Rref-b are inserted between the non-inverting input terminal of the operational amplifier 11 and the reference voltage source Vref. In addition, the switch SW2, which selects a resistor, is inserted between the resistor Rref-b and the reference voltage source Vref.
In the voltage amplification circuit 20, the output terminal of the operational amplifier 11 is connected to the non-inverting input terminal of the operational amplifier 12. A reference voltage source Vref is connected to the inverting input terminal of the operational amplifier 12, via the resistor R1. The resistor R2 is connected between the inverting input terminal and the output terminal of the operational amplifier 12.
In the received-light amplifier having the above-mentioned structure, in the case where, for example, the switch SW1 is turned OFF and only the feedback resistor Rg-a is selected in order to select a conversion efficiency mode of a particular current-voltage conversion efficiency, only the feedback capacitor Ca operates so that the frequency characteristic is optimized. For example, in the case where the switch SW1 is turned ON and both the feedback resistor Rg-a and Rg-b are selected in order to select a conversion efficiency mode of another current-voltage conversion efficiency, the feedback capacitor Ca and Cb operate simultaneously and the frequency characteristic is optimized.